Oscillatory screening apparatus with vertical screen channel

ABSTRACT

The side walls of an oscillatory screening box support a pair of associated screens defining therebetween a vertical screening channel of funnel shape. Granular material is gravity fed through the channel to an open outlet and a transverse screening motion is simultaneously imparted to the flowing material to screen fines out of the material through the screens. The oscillating drive for the assembly oscillates the same in a direction transverse to the vertical feed direction while maintaining an equilibrium of the mass.

United States Patent Schober Nov. 6, 1973 1 OSCILLATORY SCREENING APPARATUS 2,178,813 11/1939 Shaler .1 209/367 WITH VERTICAL SCREEN CHANNEL 2,445,175 7/1948 Nittson 209/362 X 2,706,047 4/1955 Dockins 1 209/360 Inventor: Johann Schober, 2,772,053 11/1956 Schmidtman 209/325 x Franz-Arnfelsergasse 16, 8200, 3,438,490 4/1969 Peterson 209/325 X Gleisdorf, Austria FOREIGN PATENTS OR APPLICATIONS [22] Wed: July 1971 10,879 6/1890 Great Britain 209/360 21 Appll 159 4 3 19,496 9/1896 Great Britain 209/360 265,658 10/1912 Germany 209/360 Related US. Application Data [631 Continuation-in-part of Ser. No. 785,489, Dec. 20, Primary Examiner Robert Halper I968 ubandmcd' Atl0rneyl(urt Kelman [30] Foreign Application Priority Data Dec. 22, 1967 Austria 11651 67 1 1 ABSTRACT The side walls of an oscillatory screening box support [52] US. Cl. 209/252, 209/360 a pair of associated Screens defining therebetween a I51] hit. Cl B07b l/28 Vertical Screening Channel of funnel Shape. Granular [58] Field Of Search 209/252, 359, 360, material is g y fed through the Channel to an p 1 339 outlet and a transverse screening motion is simulta- I neously imparted to the flowing material to screen References C'ted 1 fines out of the material through the screens. The os- UNITED STATES PATENTS cillating drive for the assembly oscillates the same in a 34 5 5 907 s 209 360 direction transverse to the vertical feed direction 2,144,382 1/1939 Lincoln 209/329 X while maintaining an equilibrium of the mass.

10 Claims, 9 Drawing Figures PATENTEU R0? 61973 SHEET 1 BF 4 FIG] WENTEBRUV 81% I 3,770.125 sum 2 m 4 OSCILLATORY SCREENING APPARATUS WITH VERTICAL SCREEN CHANNEL REFERENCE TO COPENDING APPLICATION This is a continuation-in-part of copending application Ser. No. 785,489, filed Dec. 20, 1968, now abandoned.

The present invention relates to improvements in oscillatory screening apparatus for granular material, particularly useful for the classification of mineral particulate material.

I have found that maximum efficiency and optimal structural design may be accomplished in an oscillatory screening apparatus comprising an oscillatory screening box consisting of wide walls, a pair of associated screens mounted on the side walls in the box and defining therebetween a substantially vertically extending screening channel, and means for delivering granular material to an open top inlet of the screening channel whereby the material is gravity fed through the channel from the inlet to an outlet in a vertical direction if the screens converge in a downward direction towards the open bottom outlet of the screening channel, and the means for imparting oscillating motion to the screening box and the screens, at least one component of the oscillating motion being in a direction transverse to the vertical feed direction of the granular material to impart to the vertically moving material a transverse screening motion, includes a drive for oscillating the screening box with the screens while maintaining an equilibrium of their mass on the support for the screening box.

A very advantageous drive is a rotating eccentric mass associated with the screening box for oscillating the same upon rotation.

To increase the efficiency of such oscillatory screening apparatus, it is necessary to drive the same so that considerable acceleration will be imparted to the particles flowing through the screening channel. It has been found that this efficiency is improved if the screen characteristic Kv is between 8 and 2S, Kv =an /9O,000, a being the oscillating amplitude in centimeters and n being the oscillating frequency in Hertz. Furthermore, the mean width s (in centimeters) of the screening channel should be determined by the equation s a'n' +a/2. For individual applications, the mean screening channel width is selected in accordance with the grain size of the material.

It has been found that high efficiency is obtained when the screening channel is kept filled with material because an insufficient amount of material in the channel reduces the sifting or screening effect while excess material overtaxes the operation of the apparatus. If not enough material is in the channel, it falls therethrough without being screened by passing fines laterally through the screens, and if too much material is fed to the channel, it overflows without screening.

These disadvantages may be readily avoided if the drive motor speed is adjustable within tolerances of percent so as to adjust the oscillating frequency correspondingly.

The above and other objects, advantages and features of the present invention will become more fully understood by reference to the following detailed description of certain now preferred embodiments thereof, taken in conjunction with the accompanying drawing wherein FIG. 1 is an elevational view of one embodiment of this invention, partly in section along line I-I of FIG.

FIG. 2 is a plan view of this embodiment;

FIG. 3 illustrates an eccentric drive for the apparatus of FIGS. 1 and 2;

FIG. 4 shows another type of advantageous eccentric drive;

FIG. 5 illustrates the coupling of two screening boxes driven by a fixed eccentric drive and forming a balanced oscillating system;

FIG. 6 shows a modification of the system of FIG. 5, one of the screening boxes being replaced by a counterweight whereon the eccenter drive is mounted;

FIGS. 7 and 8 illustrate details of devices for fixing the screen covers permitting not only their tensioning during operation but also a change in the screening slot width when the apparatus is at rest; and

FIG. 9 schematically shows the screening operation.

Referring now to the drawing, wherein like reference numerals indicate like parts functioning in a like manner in all figures, and more particularly to FIGS. 1 and 2, there is shown a rectangular base frame 1 from whose corners extend four uprights 2. Each upright consists of two oppositely positioned channel or U- shaped upright members 20, 2b wherebetween there are secured pairs of cylindrical rubber clamping bodies 3. A pair of screening box carriers 4 have their ends clamped between cooperating rubber bodies 3 of transversely adjacent uprights. The screening box 5 is a rigid prismatic body consisting of side walls 5a, 5a and 5b, 5b and open on top and bottom. Two pairs of screens 6 are mounted in the screening box 5, each pair of screens extending in planes slightly converging towards the bottom of the box. Each pair of screens defines a vertical screening channel s.

Since the screening box carriers are resiliently mounted on the uprights by means of rubber clamping bodies 3, 3, the box, and the screens mounted therein, is capable of oscillating or vibrating in the planes of carriers 4. This mounting of screening boxes is well known in this type of apparatus and, therefore, requires no further explanation to those skilled in the art.

The screening box is driven by a motor 12 mounted on support 14, and a suitable transmission, including a belt drive, connects the output shaft of motor 12 to a pulley at one end of rotary shaft 8 whose other end carries an eccentric mass 9. The shaft 8 is joumaled for rotation in screening box 5. The support 14 rests on preferably resilient legs 15, for instance of rubber.

The operation of the above-described apparatus will be described in connection with FIG. 3. The disc 9 at one end of the drive shaft 8 has an eccentrically arranged mass or weight 16. The point of gravity of this mass is at G. The point of gravity of the entire screening box, including the screens, lies in the axis of shaft 8 at C When the disc 9 is rotated by the shaft, a rotating vector V is produced as a result of the centrifugal force engendered by eccentric mass 16. This causes the entire system to rotate about an axis of gravity through point C in a circle indicated by B. Each point of the system rotates in such an orbital motion. The radius of the circles of motion of the system depends on the ratio of the mass of the weight 16 to the mass of the screening box as well as the rotational speed of disc 9. This ratio is so selected that (l) Kv being the screen characteristic constituted by the ratio an /90,00O, a being the oscillating amplitude in centimeters and n being the oscillating frequency in Hertz. The mean screening channel width s (in centimeters) is adjusted to meet the following equation:

Kv, s and a are selected in each instance to meet the requirements of the specific screening process and the grain size of the material to be screened, their values being experimentally established.

Since the circle of motion B is always of relatively small diameter (of an order of magnitude of about 5 to 20 mm), it is not difficult to impart this circular motion to the screening box although the drive motor 12 and its support 14 do not participate in this motion. Suitable transmission for this purpose are also well known to those skilled in the art so that a detailed description thereof is not required.

The mass of a vibratory system of this type is well balanced, i.e. little force is transmitted to base frame I, the uprights 2 or the legs 15. Thus, the supports for the system require no special considerations. Only at the beginning and the end of the vibration is there a tendency to excessive oscillating amplitudes but this phenomenon is well known in oscillating screening apparatus and can be held within acceptable limits by conventional means forming no part of the present invention and, therefore, not described herein.

Since significant unbalances in the distribution of the mass during vibration would require unacceptably massive support means for the apparatus, the equilibrium or balance of the vibrating mass is of utmost importance, particularly since the screening apparatus of this invention is designed particularly for use at provisional sites where heavy supports are not available.

The granular material to be screened in the vibratory screening box is delivered to the screens by a fixed hopper 20 (omitted from FIG. 2) whose outlet is aligned with the screening channel defined by each pair of screens 6 to be gravity-fed from above into the slot. The delivery rate is so selected that the slot is filled along its entire length but no granular material overflows out of the screening channel. If the screening channel is not full of granular material, the efficiency of the screening will be impaired, and if too much granular material is fed into the channel, it will overflow. If this happens and for this purpose, a guide plate 21 connects the upper edge of the pair of screens to which the granular material is delivered to the other pair of screens so that the overflowing material is fed into the screening channel defined by the latter screens (see FIG. 1).

The oscillating or vibratory screens 6 will impart lateral impacts to the granular material moving vertically therethrough by gravity. While the material thus flows through the screening channel, fines will pass laterally outwardly through the meshes of the screens while those grains larger than the screen mesh size will be thrown back and forth between the vibratory screens until they finally are discharged from the screening channel at the bottom, the converging screens making the channel funnel-shaped.

Conventional means (not shown) are arranged to receive and convey the screened granular material, including, if desired, conveyor bands, screw conveyors or like conventional apparatus, none of which forms part of the present invention.

When an orbital motion is imparted to the screening box in the manner hereinabove described, the screening process will take the following course, as shown in FIG. 9:

The screens 6 (extending in planes perpendicular to the plane of the drawing) rotate so that all points of the screens undergo the orbital motion indicated by circle B in FIG. 3, which motion is illustrated in FIG. 9 in connection with one point P of the screens. Assuming that a fine grain contacts a screen at this point and passes therethrough, a certain time will pass between contact of the grain with the screen and its passage therethrough. During this lapse of time, the point P has moved to P The mesh at this point is then again ready to receive and pass another fine grain, the same time elapsing again until the grain actually passes through the screen, the elapsed times between contact and passage being indicated by the angles B. However, while the screen mesh rises only by distance a during the first lapse of time, it has risen by distance a, by the time the second fine grain has passed through the screen. Thus: the deeper the screen penetrates into the material M to be sifted, the higher it rises. The probability of a grain passing through the screen increases if the screen motion includes an upwardly directed component. Therefore, the progressive penetration of the screen into the granular material will improve the screening. This partially explains the outstanding efficiency of the present screening apparatus. The path X-Y (FIG. 9) is of decisive importance to the screening results because the screen enters into the material stream M only along this path while it is retracted therefrom along the path Y to X. The material flow is pressed along this path against the illustrated screen by the opposite screen (not shown in FIG. 9).

While orbital screen motion has been found to have a good effect on the screening efficiency, good results have also been obtained with vibratory motions of other shapes, including rectilinear oscillations. FIG. 4, for instance, shows an embodiment wherein the screening box 30 oscillates only in a horizontal direction.

While only one screening channel defined by a pair of screens 6, 6 is shown, the apparatus would obviously operate in the same manner if the screening box held a plurality of screening channels, such as shown in the embodiment of FIGS. 1 and 2. The screening box is suspended from a support structure 32 by a pair of leaf springs 31, 31 enabling the screening box to oscillate or swing in a horizontal direction. The vibratory drive comprises a pair of rotating discs 33, 33 with eccentric mass distribution, the discs being rotated so that the mass distribution of the discs is always symmetric in re spect to a horizontal plane passing through the point of gravity S of the screening box. The two discs rotate in opposite directions like two meshing gears. The vectors V engendered by the centrifugal force of the eccentric masses 34 can be divided into a vertical force V and a horizontal force V Since the two vertical forces extend in opposite directions, they cancel each other. On the other hand, the horizontal forces are cumulative, changing in direction as the eccentric masses 34 are to the left or the right of the point of gravity S. In this manner, a rectilinear oscillating movement is imparted to the screening box while an equilibrium or balance of the mass of the entire system is maintained. If desired, the leaf springs 31 could be replaced by other types of suspension means.

FIG. 5 schematically shows an embodiment wherein two like suspended screening boxes 40 are coupled to a fixed crank shaft 42 by means of connecting rods 41. This will impart horizontal oscillations in opposite directions to the two screening boxes so that the entire system will maintain a mass balance. Each screening box constitutes a swinging counterweight to the other box.

This system is modified in the embodiment of FIG. 6 wherein a single screening box 50 is suspended for horizontal oscillation from support structure 32 while a suspended counterweight 51 carries the crank shaft 52 whose rotary motion is transmitted to the screening box by connecting rod 53 linking the crank shaft to the box. Again, the oscillatory motions are substantially rectilinear. In practical operations, it has been found useful to make the width of the vertical screening channel adjustable. Any suitable adjustment means may be utilized for changing the distance between the screens of each pair and for securing the screens at the adjusted spacing. For instance, the screen frames may be mounted in horizontal guides in the screening box walls for slidable movement.

In the screen adjustment arrangement illustrated in FIGS. 7 and 8, the screens 60 are mounted on tubes 61 provided with mounting hooks 62. The screens are tensioned by turning the tubes 61, to which the screen edges are attached, on their cores 63. Set screws 64 serve to fix the position of the tubes in respect of their cores. The cores have stub axles 65 positioned eccentric to the core axes and journaled in the side walls of the screening box. When nuts 66 are loosened, the stub axles 65 may be rotated so as to change the relative lateral position of the screens, i.e. to change not only the mean screening channel widths from a maximum to a minimum but also to change the convergence of the channel towards the bottom.

In a specific example, the apparatus of FIGS. 1 and 2 has been arranged for screening coke having a grain size from fines close to zero diameter to grains or particles of 20 mm diameter. It was desired to screen out all particles up to a diameter of 3 mm, which constituted the fines in this example, while the particles from 3 to 20 mm diameter were to be passed down the screening channel. The coke had a water content of about to percent. The oscillating amplitude a was 0.9 cm, i.e. a total swing of 18 mm. The mean width s of the screening channel accordingly was 32.8 mm (a'n' a/2). The rpm of the drive shaft was 1,300, resulting in a screen characteristic (0.9 l,300 /90,0O0) of 15.2. The screens defining the screening channel had a height of 120 cm and a width of 65 cm. The output was about 50 cu.m. of coke/hour, constituting about a tripling of the output obtained by conventional screening arrangements. The drive input was 11 kW.

I claim:

1. An oscillatory screening apparatus for screening mineral granular material, comprising 1. an oscillatory screening box consisting of side walls;

2. a pair of associated screens mounted on the side walls in the box and defining therebetween a substantially vertically extending screening channel, a. the screens converging in a downward direction towards an open bottom outlet of the screening channel;

3. means for delivering the granular material to an open top inlet of the screening channel at a rate such that the said channel is filled with material along its entire length, whereby the material is gravity fed through the channel from the inlet to the outlet in a vertical direction; and

4. means for imparting oscillating motion to the screening box and the screens, at least one component of said motion being in a direction transverse to the vertical feed direction of the granular material to impart to the vertically moving material a transverse screening motion, said oscillating means including a. a drive for oscillating the screening box with the screens while maintaining an equilibrium of their mass.

2. The oscillatory screening apparatus of claim I, further comprising a support for the screening box, the oscillating drive comprising a rotating eccentric mass arranged to impart to all points of the oscillating screening box and screens orbital paths in planes extending perpendicularly to the screens during oscillation.

3. The oscillatory screening apparatus of claim 1, further comprising a support for the screening box, the oscillating drive comprising a pair of rotating eccentric masses arranged in superposed vertical relationship for rotation in opposite directions to impart to all points of the oscillating screening box and screens substantially rectilinear oscillating paths extending horizontally in planes perpendicular to the screens during oscillation.

4. The oscillatory screening apparatus of claim 1, further comprising a support, two of said screening boxes with screens suspended from the support for synchronous oscillatory motion in a horizontal direction opposite to each other, the oscillatory motion being substantially rectilinear and extending in planes perpendicular to the screens during oscillation, and the oscillating drive comprising a fixed crank shaft means.

5. The oscillatory screening apparatus of claim 11, further comprising a support, a carrier for the oscillating drive, the screening box with the screens and the carrier being suspended from the support for synchronous oscillatory motion in a horizontal direction opposite to each other, the oscillatory motion being substantially rectilinear and extending in planes perpendicular to the screens during oscillation, and the oscillating drive comprising a crank shaft means.

6. The oscillatory screening apparatus of claim 1, wherein the screen characteristic Kv is between 8 and 25, Kv being the ratio of an /90,00O, a being the oscillatory amplitude in centimeters and n being the oscillatory frequency in Hertz.

7. The oscillatory screening apparatus of claim 1, wherein the mean width of the screening channel s arr +a/2, a being the oscillatory amplitude in centimeters.

8. The oscillatory screening apparatus of claim I, wherein the drive includes a rotary shaft, the rotary speed of the shaft being adjustable to adjust the oscillating frequency.

flowing material from this screening channel to the screening channel of the screening channel of the other pair of screens.

10. The oscillatory screening apparatus of claim 1, further comprising means for adjusting the width of the screening channel. 

1. An oscillatory screening apparatus for screening mineral granular material, comprising
 1. an oscillatory screening box consisting of side walls;
 2. a pair of associated screens mounted on the side walls in the box and defining therebetween a substantially vertically extending screening channel, a. the screens converging in a downward direction towards an open bottom outlet of the screening channel;
 3. means for delivering the granular material to an open top inlet of the screening channel at a rate such that the said channel is filled with material along its entire length, whereby the material is gravity fed through the channel from the inlet to the outlet in a vertical direction; and
 4. means for imparting oscillating motion to the screening box and the screens, at least one component of said motion being in a direction transverse to the vertical feed direction of the granular material to impart to the vertically moving material a transverse screening motion, said oscillating means including a. a drive for oscillating the screening box with the screens while maintaining an equilibrium of their mass.
 2. a pair of associated screens mounted on the side walls in the box and defining therebetween a substantially vertically extending screening channel, a. the screens converging in a downward direction towards an open bottom outlet of the screening channel;
 2. The oscillatory screening apparatus of claim 1, further comprising a support for the screening box, the oscillating drive comprising a rotating eccentric mass arranged to impart to all points of the oscillating screening box and screens orbital paths in planes extending perpendicularly to the screens during oscillation.
 3. means for delivering the granular material to an open top inlet of the screening channel at a rate such that the said channel is filled with material along its entire length, whereby the material is gravity fed through the channel from the inlet to the outlet in a vertical direction; and
 3. The oscillatory screening apparatus of claim 1, further comprising a support for the screening box, the oscillating drive comprising a pair of rotating eccentric masses arranged in superposed vertical relationship for rotation in opposite directions to impart to all poInts of the oscillating screening box and screens substantially rectilinear oscillating paths extending horizontally in planes perpendicular to the screens during oscillation.
 4. The oscillatory screening apparatus of claim 1, further comprising a support, two of said screening boxes with screens suspended from the support for synchronous oscillatory motion in a horizontal direction opposite to each other, the oscillatory motion being substantially rectilinear and extending in planes perpendicular to the screens during oscillation, and the oscillating drive comprising a fixed crank shaft means.
 4. means for imparting oscillating motion to the screening box and the screens, at least one component of said motion being in a direction transverse to the vertical feed direction of the granular material to impart to the vertically moving material a transverse screening motion, said oscillating means including a. a drive for oscillating the screening box with the screens while maintaining an equilibrium of their mass.
 5. The oscillatory screening apparatus of claim 1, further comprising a support, a carrier for the oscillating drive, the screening box with the screens and the carrier being suspended from the support for synchronous oscillatory motion in a horizontal direction opposite to each other, the oscillatory motion being substantially rectilinear and extending in planes perpendicular to the screens during oscillation, and the oscillating drive comprising a crank shaft means.
 6. The oscillatory screening apparatus of claim 1, wherein the screen characteristic Kv is between 8 and 25, Kv being the ratio of an2/90,000, a being the oscillatory amplitude in centimeters and n being the oscillatory frequency in Hertz.
 7. The oscillatory screening apparatus of claim 1, wherein the mean width of the screening channel s a pi +a/2, a being the oscillatory amplitude in centimeters.
 8. The oscillatory screening apparatus of claim 1, wherein the drive includes a rotary shaft, the rotary speed of the shaft being adjustable to adjust the oscillating frequency.
 9. The oscillatory screening apparatus of claim 1, comprising two of said pairs of associated screens arranged parallel to each other in the screening box, a material supporting surface interconnecting the upper edges of said pairs of associated screens, and the material delivering means being arranged to deliver the material to the screening channel of one of said pairs of screens, the material supporting surface guiding overflowing material from this screening channel to the screening channel of the screening channel of the other pair of screens.
 10. The oscillatory screening apparatus of claim 1, further comprising means for adjusting the width of the screening channel. 